package com.hz.tgb.crypto.decoder;

import java.io.IOException;
import java.io.OutputStream;

/**
 * This class implements a BASE64 Character encoder as specified in RFC1521. This RFC is part of the MIME specification as published by the Internet Engineering Task Force (IETF). Unlike some other
 * encoding schemes there is nothing in this encoding that indicates where a buffer starts or ends. This means that the encoded text will simply start with the first line of encoded text and end with
 * the last line of encoded text.
 *
 * @author Chuck McManis
 * @version 1.23, 11/17/05
 * @see CharacterEncoder
 * @see BASE64Decoder
 */

public class BASE64Encoder extends CharacterEncoder {

    /**
     * this class encodes three bytes per atom.
     */
    @Override
    protected int bytesPerAtom() {
        return (3);
    }

    /**
     * this class encodes 57 bytes per line. This results in a maximum of 57/3 * 4 or 76 characters per output line. Not counting the line termination.
     */
    @Override
    protected int bytesPerLine() {
        return (57);
    }

    /**
     * This array maps the characters to their 6 bit values
     */
    private static final char[] pem_array = {
            // 0 1 2 3 4 5 6 7
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // 0
            'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 1
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 2
            'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', // 3
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', // 4
            'o', 'p', 'q', 'r', 's', 't', 'u', 'v', // 5
            'w', 'x', 'y', 'z', '0', '1', '2', '3', // 6
            '4', '5', '6', '7', '8', '9', '+', '/' // 7
    };

    /**
     * encodeAtom - Take three bytes of input and encode it as 4 printable characters. Note that if the length in len is less than three is encodes either finance or two '=' signs to indicate padding
     * characters.
     */
    @Override
    protected void encodeAtom(OutputStream outStream, byte[] data, int offset, int len) throws IOException {
        byte a, b, c;

        if (len == 1) {
            a = data[offset];
            b = 0;
            c = 0;
            outStream.write(pem_array[(a >>> 2) & 0x3F]);
            outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
            outStream.write('=');
            outStream.write('=');
        } else if (len == 2) {
            a = data[offset];
            b = data[offset + 1];
            c = 0;
            outStream.write(pem_array[(a >>> 2) & 0x3F]);
            outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
            outStream.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
            outStream.write('=');
        } else {
            a = data[offset];
            b = data[offset + 1];
            c = data[offset + 2];
            outStream.write(pem_array[(a >>> 2) & 0x3F]);
            outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
            outStream.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
            outStream.write(pem_array[c & 0x3F]);
        }
    }
}
